1. Field of the Invention
The present invention relates to an image processing method and an image processing device for creating composite image information in which sub information (e.g., security information) is invisibly embedded in main image information like a human facial image or reconstructing the sub information from the composite image information.
2. Description of the Related Art
Recently, with a trend toward electronization of information and proliferation of the Internet, technologies such as electronic watermarking or electronic signature are attracting public attention to prevent counterfeiting and alteration of images. Particularly, an electronic watermarking technique for embedding additional sub information (e.g., security information) in main image information (e.g., human facial image) has been used as a countermeasure against unauthorized copying, counterfeiting, and tampering of an ID card or a photograph with copy right information embedded therein.
For example, Japanese Patent No. 3547892 (Document 1) discloses an electronic watermarking inserting technique for embedding data as sub information into image data as main image information which is to be printed on a recording medium by using characteristics of a high spatial frequency component and a color difference component which a human being is difficult to recognize.
However, in the above-mentioned Document 1, only contour information of sub information is principally embedded into main image information. Therefore, information reconstructed as sub information is only contour information. That is, information other than contour information, such as density information is not reconstructed by the electronic watermarking technique disclosed in Document 1. For this reason, the electronic watermarking technique disclosed in Document 1 is not suitable for a type for reconstructing two-dimensional image information like a two-dimensional code as sub information.
Jpn. Pat. Appln. KOKAI Publication No. 2005-184603 (Document 2) discloses an electronic watermarking technique in which a two-dimensional code which is two-dimensional image information is used as sub information. However, information represented by a two-dimensional code is not information which can be understood directly by a human being. That is, it is difficult for a human being to directly discriminate whether image information of a reconstructed two-dimensional code is proper or not.